Cancer is America's second leading cause of death. Approved anticancer agents, both chemotherapeutic and targeted agents, are limited by toxicity and are ultimately ineffective against solid tumors, e.g.: lung, colorectal, breast, pancreatic, and prostate cancers, which account for more than 85% of cancer deaths. To kill tumors using the body's immune system, the failure of which has allowed the cancer to emerge, has long been the goal of cancer research. Val-boroPro, also known as PT-100 or talabostat, is a dipeptide boronic acid that showed remarkable efficacy in shrinking tumors in mice through immune activation. However, in Fast Track Phase III clinical trials, it did not meet its objectives, due to dose-limiting toxicity.
The US Food and Drug Administration approved the first cancer vaccine, Provenge for prostate cancer, on Apr. 29, 2010. Provenge is a dendritic cell therapy (DCT); one of several exciting new immunotherapies sometimes called “cancer vaccines”. By supercharging the immune system, such vaccines can, in principle, find and remove the very last cancer cell, no matter where it hides, thus precluding mere remission after a course of treatment. Although the concept is now proven, cancer vaccines, including DCTs other than Provenge, have failed to achieve the desired efficacy in clinical trials, indicating the need to add immune stimulators, or adjuvants. However, less toxic adjuvants are needed to develop this approach clinically.